Zugunruhe, the Restlessness of a Bird Who Has Never Left the Cage

In autumn at Andechs, Bavaria, garden warblers (Sylvia borin) in cages hopped and whirred their wings in the dark while Eberhard Gwinner watched. The German word for it is zugunruhe, “migratory restlessness”: night-time activity in caged migratory birds during the seasons when wild ones of their species migrate.

How does a bird keep a calendar without seasons?

Gwinner kept his warblers for three years under constant day length. With no shortening sunsets, the birds kept cycling through migratory restlessness and moult on their own schedule, with periods of roughly 9 to 13 months instead of a year. The calendar was inside them, running a little fast. Johann Andreas Naumann is credited with first describing the restlessness in caged birds.

Does a person have anything like it?

Nothing in this research tests people. Waking in the dark just before an alarm resembles it only in shape: an internal timer acting with no cue in the room. That experience has its own literature under anticipatory waking, and the two calendars visibly disagree after clock changes.

Which way does the bird face?

Gustav Kramer reported in 1949 that the restlessness is aimed. Caged birds point toward the heading that wild ones of their species would fly.

Small questions

How is zugunruhe measured?

Kramer’s 1949 work relied on watching the cage. Stephen and John Emlen’s 1966 funnel cage automated it: an indigo bunting stood on an ink pad, and the marks on the sloped walls recorded which way it fluttered.

Do stars steer it?

Stephen Emlen alone ran the 1967 planetarium experiments with indigo buntings. The marks followed the star pattern around the North Star, and when he shifted that pivot east or west, the marks shifted with it.

Does zugunruhe apply to humans?

No. The research covers birds only, and no study of it has tested people. Comparing it to waking before an alarm is an analogy, not a finding.